1. Technical Field
The present application relates to a surface-modified semiconductor including a gallium nitride semiconductor, of which the principal surface is either a non-polar plane or a semi-polar plane, and also relates to a method of arranging a plurality of particles on the surface of a semiconductor.
2. Description of the Related Art
Affinity of a liquid for the surface of a solid is called “wettability”. To control the wettability is an important process step in a process using a liquid phase. Among other things, in performing a photolithographic process step of a semiconductor device manufacturing process, it is very important to control the hydrophilicity and hydrophobicity of the surface of a semiconductor wafer. That is why there is a growing demand for a technique for controlling hydrophilicity and hydrophobicity at as low a cost and in as short a process time as possible. However, as for a gallium nitride based compound semiconductor (which will be referred to herein as a “GaN-based semiconductor” and which is represented by the general formula: AlxGayInzN (where 0≦x, y, z≦1 and x+y+z=1)), no effective measure has been found yet.
A GaN-based semiconductor has a wurtzite crystal structure. FIG. 1 schematically illustrates a unit cell of GaN. In an AlxGayInzN (where 0≦x, y, z≦1 and x+y+z=1) semiconductor crystal, some of the Ga atoms shown in FIG. 1 may be replaced with Al and/or In atoms.
FIG. 2 shows the primitive vectors a1, a2, a3 and c of a wurtzite crystal structure. The primitive vector c runs in the [0001] direction, which is called a “c-axis”. A plane that intersects with the c-axis at right angles is called either a “c-plane” or a “(0001) plane”. Furthermore, a plane which is terminated with a Group III element such as Ga is called either a “+c-plane” or a “(0001) plane”, whereas a plane which is terminated with a Group V element such as nitrogen is called either a “−c-plane” or a “(000-1) plane”. That is to say, these two crystal planes are dealt with as different ones. It should be noted that the “c-axis” and the “c-plane” are sometimes referred to as “c-axis” and “C-plane”.
In the present specification, the “m-plane” refers herein to a (10-10) plane that is perpendicular to the [10-10] direction. In the present specification, “−” attached on the left-hand side of a Miller-Bravais index in the parentheses means a “bar” (a negative direction index). As shown in FIG. 2, the m-plane is parallel to the c-axis and intersects with the c plane at right angles. In this case, the “m-plane” is a generic term that collectively refers to a family of planes including (10-10), (−1010), (1-100), (−1100), (01-10) and (0-110) planes.
In the present specification, the “a-plane” refers herein to a (11-20) plane, which intersects with the [11-20] direction at right angles. As shown in FIG. 3C, the a-plane is parallel to the c-axis and intersects with the c-plane at right angles. In this case, the “a-plane” is a generic term that collectively refers to a family of planes including (11-20), (−1-120), (1-210), (−12-10), (−2110) and (2-1-10) planes.
In the present specification, the “+r-plane” refers herein to a (10-12) plane, which intersects with the [10-12] direction at right angles. The r-plane is shown in FIG. 3D. In this case, the “+r-plane” is a generic term that collectively refers to a family of planes including (10-12), (−1012), (1-102), (−1102), (01-12) and (0-112) planes.
In the present specification, the “−r-plane” refers herein to a (10-1-2) plane, which intersects with the [10-1-2] direction at right angles. In this case, the “−r-plane” is a generic term that collectively refers to a family of planes including (10-1-2), (−101-2), (1-10-2), (−110-2), (01-1-2) and (0-11-2) planes.
PCT International Application Publication No. 2009/014590 discloses a technique for subjecting an ink composition having semiconductor nano-crystals including a mixture or alloy of GaN to an ultraviolet ray treatment. The ultraviolet ray treatment disclosed in PCT International Application Publication No. 2009/014590 uses an ultraviolet ray's effect of cross-linking a functional unit by acting on the functional group of a liquid medium which forms part of the ink composition, not on the GaN semiconductor crystals, and therefore, is not a technique for modifying the GaN semiconductor crystals themselves.
Japanese Laid-Open Patent Publication No. 2008-183702 discloses a technique for exposing a pattern forming substrate, including a surface-modified layer having a functional group that has affinity for GaN nano-crystals, to an ultraviolet ray. The ultraviolet ray exposure technique disclosed in Japanese Laid-Open Patent Publication No. 2008-183702 does not act on the GaN crystals but uses the effect of heating in transferring those GaN crystals from a stamper to the surface-modified layer. That is why this is not a technique for modifying GaN crystals themselves, either.
PCT International Application Publication No. 2005/119862 discloses a technique for irradiating a member of a GaN-based semiconductor laser device with an ultraviolet ray. The ultraviolet ray irradiation technique disclosed in PCT International Application Publication No. 2005/119862 does not act on GaN-based semiconductor but is just used to remove Si-containing substances or hydrocarbon from the member of the GaN-based semiconductor laser device. That is why this is not a technique for modifying the GaN-based semiconductor itself, either.